In next-generation cellular communication systems, the use of millimeter-wave communications is highly likely due to the lack of available spectrum at lower frequencies. In these types of systems, in order to establish stable signal paths between user equipment and base stations, high-gain antenna arrays are likely to be mandatory in order to compensate for link losses and reduce power consumption at both ends. To minimize losses due to polarization mismatches between user equipment and base stations, circular polarization (CP) or dual linear polarization (LP) can be used in the base stations' antenna arrays.
In order to enable millimeter-wave cellular systems, phased antenna arrays may be employed at both base stations and user equipment to improve signal-to-noise ratios through beam forming. On the base station side, multiple planar antenna arrays capable of steering within specific sector areas could be used to cover a cell. On the user equipment side, the coverage requirement is often much more rigorous. Due to the unpredictable location and position of a base station with respect to the user equipment, the user equipment's antenna array may need to be able to steer its beam in any arbitrary direction and cover the entire space around the user equipment.